(a) Field of the Invention
This invention relates to microscopes and more particularly to a microscope provided with an automatically controlled illuminating optical system.
(b) Description of the Prior Art
Generally, the greatest factor for determining the optical performance of a microscope is the optical performance of objectives themselves. However, unless the illuminating light incident upon the objective is proper, the perfomance of the objective will not be able to be well utilized. Therefore, in the case of a high performance microscope, it will be necessary to properly correct the illuminating light with the change of the objective by switching over the condenser lens of the illuminating optical system and adjusting the aperture stop and field stop. In such case, as the conditions on the visual field and numerical aperture must be met, in order to make a proper illumination of from a very low magnification to a high magnification, the switching over of the condenser lens will be made by a stepwise switching or zoom type switching. When the aperture stop is opened to be too large, the contrast of the object image will reduce but, when it is stopped down to be too small, the resolving power will reduce. However, it is generally considered to be the best to stop down the aperture stop to be a little smaller than the pupil of the objective. At the time of photographing, if it is stopped down to be a little smaller than at the time of observation, a better result will be obtained. Further, if the field stop is stopped down to be smaller, the contrast of the center will improve. Therefore, it is stopped down as much as possible to be so small as not to cut the visual field. The brightness of the visual field will vary so greatly depending on the magnification of the objective to be used and the illuminating optical system that the light must be adjusted by the adjustment of the light source voltage and the insertion of an ND-filter. Thus, in order to make display the performance of the microscope to be used, such complicated and difficult operations as are mentioned will be required whenever the objective is changed. By the way, as a prior art, there is such microscope illuminating device as is disclosed in Japanese Patent Publication No. 44923/1980. This is only to operatively connect the change of the illuminating lens system with the change of the objective and little contributes to the simplification of the entire microscope.